Polyaminopolyamide-epichlorohydrin wet-strength resins contain significant amounts of chloro-alcohols derived from side reactions of epichlorohydrin. Not being cationic polymers, these chloro-alcohols are not retained on paper pulp as are the cationic polymeric wet-strength resins. They remain largely in the water and enter the environment principally through mill waste water. There is concern about organic chloride compounds entering the environment in such effluents from industrial processes.
In the conventional manufacture of polyaminopolyamide-epichlorohydrin ("polyamide-epi") wet-strength resins, prepolymer in aqueous solution is reacted with epichlorohydrin (epi) at between about 20.degree. C. and 85.degree. C., more typically between about 50 C. and 80.degree. C., to produce the desired solution viscosity, and the solution is diluted and/or acidified to stabilize the resin product.
Not all of the epi in the aqueous reaction mixture reacts with amine groups to functionalize the polymer; some of the epi reacts with water to form 3-chloropropane-1,2-diol ("CPdiol"), and some epi reacts with chloride ion to form dichloro-2-propanol (DCP), normally a mixture of 1,3-dichloro-2-propanol and 2,3- -dichloro-1-propanol, both of which are toxic by-products. Furthermore, the formation of DCP lowers the effective utilization of epichlorohydrin to form polyamide-epichlorohydrin resin.
It is known to recover the DCP and reconvert it to epi for recycle by repeated batch extraction or counter-current extraction of the resin solution, but these procedures are expensive and may not be cost-effective.
It would be desirable to have a cost-effective process for substantially reducing the concentration of epichlorohydrin and its by-products in polyamide-epichlorohydrin resin solutions.